I've redrawn the circuit diagram with a few planned updates. What I'm stuck on is:
Question 1: Choosing values and types of fuse for the input mains side of the power supplies:
3 power supplies requiring input protection are:
1. Planned new linear supply for X, A, Y axes, @750VA, pulling up to 9A (4.1A parallel 3.1Nm steppers x 3off x 70%)
2. Existing SMPS for Z axis is 350W pulling about 1-2A (2A series 1.8Nm stepper x 1off x 70%)
3. Existing SMPS for ancillaries is 12V, 60W, 5A
What to choose for each of the 3 above power supply mains inputs:
> Use MCB din rail mounted double throw?
> What type (A,B,C,D) to choose to avoid trip on inrush?
> What current level to choose?
Question 2: Choosing fuse values for DC output side of supplies
1. Linear supply on X,A,Y could pull up to 4A per motor - choose 5A blade fuse to each stepper?
2. SMPS on Z could pull up to 2A - choose 3A blade fuse?
3. SMPS for ancillaries rated at 5A - just go with 5A blade fuse?
If it helps here is the updated schematic, with the required new fuses / MCBs shown in RED (ignore ratings and type, those are some ideas which I'd like confirming):
Question 3: Setting current rating on DQ860MA drivers
Stepper motors are rated at 2.1A per phase so 4.2A total. Current setting options are either PEAK or RMS. Which to choose on the driver dip settings? Is it 4.2A PEAK or 4.0A RMS?
Question 4: Do the toriod and power regulator calcs in the previous post seem OK?
Sorry for all the questions . . .
I ordered the toroid (750VA, 2x24v), power regulator board (60,000uF 100V capacitors, 20A rectifier), double pole MCBs for each power supply of various current rating with type D trip, DIN rail, DC fuse box holders.
Whilst waiting for this stuff to arrive I looked again at the blown SMPS and noticed a tiny glass fuse tucked away in the corner and soldered direct to the PCB (F2 - photo shows it removed).
It was clearly blown with black on the glass. I managed to cut the legs and get it out to read the rating and it looked like 250V 15A (printing was faint so not sure) about 3.5mm wide and 10mm long. Bit of searching revealed it was called an axial lead fuse and only they cost a few pounds for a pack of 4. Started to wonder if I could repair it and get the machine running for now until the linear supply was here and built. So I took the board out but discovered alot of damage underneath, some of them were charred surface mounted components. Even if I replaced the fuse and it worked would I trust it? Decided not.
So I need to wait a few weeks for all the new linear bits to arrive. No doubt I'll post any questions I have at that time so I don't get any more blue flashes. All for now.
All the bits arrived in double quick time. Now I need some help confirming the wiring colours and general connections.
Here is the toroid: 750VA 2x24 from airlink
Here is the power regulator (60,000uF, 100V, 20A rectifier):
Here is a circuit I've drawn up but need help with:
1. Toroid blue and brown I assume are mains input?
2. 4 output wires are from the pair of windings? - but which to connect to the regulator and in which order?
3. I'll mount all this on an aluminium plate which will go to earth - does the centre GND output on the DC side need to be earthed as well?
I'm away from the parts at the moment otherwise I would at least give you the resistance readings across the toroid wires, but hopefully the above is enough.
I had similar parts wired like that http://www.mycncuk.com/threads/7659-...9481#post59481
Hope that helps
Thank you for that link - very good reading. Based on Jonathan's comments and your selection of the 40,000uF model then based on Neil's suggestion then you might only be getting 10,000uF (10,000uF x 2 /2). Any issues with running like that on your machine? If I use my board as-is then I'll only get 15,000uF.
Thank you. I briefly looked at the toroid when it arrived to make sure all was intact and didn't notice the sticker on the side!
As for modifying the board to get the full 60,000uF - the tracks are 'painted over' ; either that or it is a multilayer board because apart from the solder points there are no exposed tracks on the top or bottom. I'd probably have to demount the capacitors and run flying leads to them from the output of the rectifier.
Had a couple of minutes spare today so checked the output from the secondary coils:
Mains was 243V AC and each secondary coil was 26.4V AC
I need to wire the secondarys in series but cannot find any markings on the cables to show which is the start of the winding. I've read that it does not matter how they are connected (unlike parallel which is vital). Can someone confirm this is the case?
For a while I had my machine running 4 motors from a 500VA transformer with 11000uF capacitance and I noticed an improvement in obtainable feedrates when I moved one motor to another (320VA) transformer and left the original transformer and capacitors with just 3 motors. So maybe 15000uF is fine ... bit subjective though as I didn't take any readings to verify.
Or we could do some sort of swap.
Thank you for taking time to write that comprehensive reply. I'd done a bit of thinking on the series connections and quickly realised that one way would be ~0V and the other way ~50V AC ! So thank you for confirming that. I'll try connecting as you suggest - its either one way or the other and at least being series it won't matter if I get it wrong.
Had another look at the regulator board and I can now see some tracks but am not confident I could make a safe job of modifying it.
So I've also decided to de-mount the capacitors and build a more conventional system. I've ordered:
Solder sucker (had one years ago but can't find it ~£4)
35mm diameter capacitor clamps (6off ~£1.50 for a pair)
400V 35A rectifier centre bolt mounted (~£3)
Thank you for the kind offer to swap / supply dwgs for the capacitor circuit but I'm going to go for the traditional route of mounting each capacitor in the plastic mounts (inverted) and solder cables between the pins. It looks like there will be about 3mm of pin remaining from the top of the caps which should be enough to a cable get onto. The rectifier will be the traditional 4 spade pin type. All bits will be mounted to a ~4mm aluminium plate for heat dissipation and general sturdiness.
That's good background info on the ripple voltage. I had started to wonder about what an acceptable level would be. More capacitors will be better with lower ripple but I guess gives more in-rush current so more chance of tripping the MCB on start up. At least I can play around with the number of capacitors if I have that problem. But if it just works then I'll leave it and get on with using the machine.
For info this is my 3rd generation of cnc machine, with many minor iterations of development along the way, but it remains my only cnc machine and is currently out of action until the PSU if fixed.
Don't you just hate black soldermask :|
If you remove three of the capacitors that are in parallel, then put them back in the other way round, you will have one terminal of all 6 connected, so just one piece of wire will be needed to connect the '+VCC' and '-VCC' terminals to have the capacitors in parallel. If you can break one track on the PCB and add one piece of wire, then you can use the existing diodes.
Thank you again. I had to draw out your idea of reversing the capacitors before I could see how it could work. I considered it for quite a while but in the end was concerned about breaking the tracks and adding flying leads. I've had enough of blue flashes and bangs.
I've managed to remove the capacitors from the board. Looks like there is plenty of remaining pin to solder the cable to:
Capacitor mounting brackets and a new rectifier should be here by the weekend so I will lay it all out on the mounting plate if I get the opportunity.
I've decided for reasons of space (6off 10,000uF caps with mounting brackets takes up a surprising amount of space!) and in-rush current to go with 40,000uF as a starting point.
I'll report back with success or more questions . . .
One more thing, I've added a safety latch relay for the spindle inhibit. This makes sure that if there is an e-stop (which stops everything including the spindle) that when the e-stop is cleared the spindle does not fire up until the start button is deliberately pressed again. Ordered 2 pole DIN relay for this job. Drawing updated:
Last edited by routercnc; 15-04-2015 at 10:02 PM.